1. Field of the Invention
The present invention relates to a data processing apparatus for coding or decoding or the like of binary data in which binary data sequence is converted to a binary code sequence which is suitable for data processes in an electronic apparatus such as a magnetic disk, optical disk, data transmitting apparatus, or the like.
2. Description of the Prior Art
Hitherto, in electronic apparatuses such as a magnetic disk, optical disk, data transmitting apparatus, or the like, it is necessary to record or transmit a great amount of information. For instance, in recording, it is inevitable to improve recording density upon the recording of binary data on a recording medium.
On one hand, in transmitting, it is inevitable to improve transmission speed. In addition, various kinds of coding and decoding systems have been proposed.
FIG. 1 is a diagram for explaining one example of conventional coding systems. FIG. 1(a) shows an example of a bit pattern of an original binary data sequence, in which numerals 0 and 1 denote bit logics "0" and "1" and T.sub.0 represents a bit interval. FIGS. 1(b) and 1(d) respectively show one example of conventional coding systems, in which the system of FIG. 1(b) is called an MFM system (Modified FM system) and the system of FIG. 1(d) is called a 3PM system (3 Position Modulation system). When the recording technology is described, as an example of the apparatuses to which the foregoing respective systems are applied, the MFM system is used in the magnetic disk apparatuses (models 3330, 3340, 3350, etc.) made by IBM Corporation and the 3PM system is used in the magnetic disk apparatus (Model 8434) made by UNIVAC Corporation. For the algorithm of each system, in case of the MFM system, the original data "1" and "0" are converted to "01" and "X0" in correspondence thereto. However, in the coded sequence after conversion, " X" becomes a plurality of logics (1.fwdarw.0, 0.fwdarw.1) of the code bit immediately before X. On one hand, for the algorithm of the 3PM system, the original data is separated on a 3-bit unit basis and is converted to 6-bit codes as shown in Table 1.
TABLE 1 ______________________________________ Coding Algorithm of the 3PM System Original Conversion data code Condition ______________________________________ 000 000010 001 000100 010 010000 When a pattern "101" is 011 010010 generated in the code 100 001000 sequence after conver- 101 100000 sion, it is converted 110 100010 to "010". 111 100100 ______________________________________
For the coded sequence converted by each of the coding systems, a recording current is produced so as to become a signal such that the magnetization inversion occurs for a bit of "1" and the magnetization inversion does not occur for a bit of "0" and is recorded on the foregoing recording medium. FIGS. 1(c) and 1(e) show waveforms (NRZI signal) of the recording currents of the code systems which were coded by the MFM system of FIG. 1(b) and by the 3PM system of FIG. 1(d).
Generally, in the recording on the magnetic medium,
(a) When the magnetization inversion interval (recording wavelength) becomes short, the magnetic transitions due to the magnetization inversions before and after this interval are mutually interfered, thereby producing a cause for occurrence of errors upon decoding of the reproduction signal.
(b) Even in the case where a demodulation phase margin (TW) (which will be explained later) upon reproduction to the recording wavelength is small, the same errors as mentioned above could be easily caused.
(c) When the recording wavelength is larger as compared with the period of the clock signal for demodulation which is produced from the reproduction signal, the above-mentioned clock cannot be produced accurately from the reproduction signal, so that the same errors as mentioned above could be easily caused.
(d) When a ratio between the maximum value and the minimum value of the magnetization inversion interval becomes large, the waveform interference (called the pattern peak shift) of the reproduction signal increases, so that the same errors as mentioned above could be easily caused.
Thus, in the general coding systems, as the parameters indicative of the capabilities including the foregoing four items (a) to (d), the following variables are given. It is now assumed that in a certain coding system, the m-bit binary data sequence is converted to the binary code sequence of n (n.gtoreq.m) bits, and the minimum value of the number of codes of "0" between the code "1" selected arbitrarily from among the code sequence after conversion and the next code "1" is d and its maximum value is k. From this assumption, we have ##EQU1## where, T.sub.0 is one original data period.
Therefore, from the above description, it is desirable that the values of equations (1) and (4) are larger (from the explanations in the foregoing items (a) and (b)). On one hand, it is preferable that the value of the demodulation clock period in equation (3), the ratio of the maximum magnetization inversion interval (equation (5)) mentioned below and the ratio between the maximum and minimum magnetization inversion intervals (equation (6)) mentioned below are smaller. ##EQU2## The above-mentioned parameters are shown in Table 2 with regard to the foregoing MFM and 3PM coding systems.
TABLE 2 ______________________________________ Parameters of Each Coding System Parameter Coding T.sub.max / T.sub.max / system T.sub.min T.sub.W C.sub.LK T.sub.min T.sub.max ______________________________________ MFM system T.sub.0 0.5 T.sub.0 4 2 2T 3PM system 1.5 T.sub.0 0.5 T.sub.0 12 4 6T FM system 0.5 T.sub.0 0.5 T.sub.0 2 2 T ______________________________________
In addition, as described above, in the general coding systems, original data is converted to the n-bit code for every m bits and is expressed as (m, n, d, k) codes in which the run length of "0" of the code after conversion is restricted to a value which is not smaller than d and not larger than k. However, the handling number m (m.ltoreq.n) of this data bit affects the hardware of the apparatus. In this case, it is generally desirable that a value of m is small. When the foregoing coding systems are expressed by the (m, n, d, k) parameters, they will become (1, 2, 0, 1) in case of the FM coding system; (1, 2, 1, 3) in case of the MFM coding system; and (3, 6, 2, 11) in case of the 3PM coding system. On one hand, what is called a DC free code of which a variation in DC component of the coded signal is suppressed is also generally desired.